The major clinical complications associated with herpes simplex virus -1 (HSV-1) infection of the eye include corneal ulcers, severe pain, inflammation, loss of corneal avascularity, and vision loss. Antiviral agents alone often fail to correct the problems because many of the disease symptoms may be signaled by infection but then regulated more directly by host molecules. This proposal studies, human heparanase (HPSE), a host enzyme that may potentially regulate both, virus growth and disease manifestations in the cornea. HPSE is a heparan sulfate (HS) endoglycosidase whose levels correlate directly with the breakdown of epithelial and endothelial basement membrane barriers, increased vascular permeability and leukocyte extravasation, and liberation of HS-bound cytokines and growth factors promoting angiogenesis and inflammation in the surrounding areas. The PI?s laboratory has recently observed a significant increase in HPSE expression and higher enzymatic activity upon HSV infection of human corneal cells, cultured human corneas, and animal models of ocular infection and demonstrated its significance in viral spread and transmission. In murine corneas HPSE upregulation directly contributes to corneal disease pathologies including ulceration, inflammation and neovascularization. In addition, we unexpectedly found that HPSE knockout cells show a severe deficiency in virus production. Therefore, based on our newly generated preliminary results we hypothesize an important regulatory role for HPSE in HSV-1 transcription and propose to establish HPSE as a key host virulence factor. We propose that activated HPSE directly adds to the severity of herpetic diseases including tissue damage and promotes viral infection and reactivation. This proposal will focus on understanding the HPSE driven mechanisms that contribute to HSV-1 growth in the cornea and demonstrating the antiviral/anti-inflammatory effects of HPSE inhibition or chromosomal deletion. Three Aims are proposed. First Aim will establish the molecular basis behind the loss of HSV-1 infection in cells lacking HPSE. It is based on our hypothesis that HPSE through its nuclear localization and complex set of interactions promote HSV-1 transcription. Second Aim will determine the significance of HPSE in HSV-1 infection of the murine cornea. This Aim will use a HPSE knockout mouse model to prove our hypothesis that HPSE is a host virulence factor that promotes HSV-1 infection in the cornea, drives tissue damage and disease pathologies, and facilitates viral spread to and return from the trigeminal ganglia (TG) during reactivation. The third and final Aim will determine the therapeutic benefits of an HPSE inhibitor against HSV-1 infection of the cornea. This Aim will prove our hypothesis that pharmacological inhibition of HPSE will result in unprecedented therapeutic benefits including quick resolution of infection and corneal inflammation. Successful conclusion of our study will help establish a brand new role for HPSE as a host virulence factor and identify new factors that help promote its pathogenic activities in the cornea. Our results will significantly enhance our understanding of HPSE functions and herpetic disease mechanisms, and accelerate new strategies to control ocular infection.